This application claims the priority of 8-055783, the disclosure of which is expressly incorporated by reference herein.
The present invention relates to a control apparatus for an automatic transmission of a vehicle and a control method for that transmission. More particularly, the invention relates to an apparatus and a method for controlling hydraulic pressure in operating an automatic transmission of a vehicle.
A known control method of the kind outlined above typically involves keeping an engaging pressure of an engaging-side frictional engaging device constant until a torque phase is approximately started for a shift-up operation, the engaging pressure getting thereafter increased for the shift, as disclosed illustratively in Japanese Patent Laid-Open No. Hei 7-27217. The torque phase refers to a period in which torque alone is varied while the engine speed remains unchanged at the start of a shift from second to third, as indicated by temporal changes of a Gf signal (to be defined later) in a timing chart of FIG. 2 of this specification. The torque phase is followed by a period called an inertia phase in which the clutch inside the transmission starts to be engaged and the engine speed drops accordingly.
There is a problem with the conventional control method such as the one disclosed in Japanese Patent Laid-Open No. Hei 7-27217. As the engaging pressure of the engaging-side frictional engaging device is being raised at shift-up time from the beginning of a torque phase, torque fluctuations are increased in the first half of the subsequent inertia phase, which makes it impossible to acquire good shift characteristics. Another problem is that during feedback control of the engaging pressure from the beginning of the torque phase, large torque fluctuations at the first half of the inertia phase tend to lower robustness (i.e., stability of the control system).
It is therefore an object of the present invention to provide an automatic transmission control apparatus and method whereby torque fluctuations in the first half of an inertia phase are placed under feed-forward control to enhance robustness in subsequent feedback control so that an improved repeatable shift characteristic is obtained.
The foregoing object may be achieved according to one aspect of the present invention, which provides an automatic transmission control method and apparatus comprising two frictional engaging devices in an automatic transmission connected to an engine, and pressure control command generation apparatus. One of the frictional engaging devices is engaged and the other device disengaged for a shift. The pressure control command generation apparatus controls hydraulic pressures supplied to the two frictional engaging devices during the shift and varies pressure control characteristics of the devices accordingly. The automatic transmission control apparatus further comprises: inertia phase recognition apparatus for recognizing an inertia phase during a shift; torque fluctuation suppression apparatus for calculating pressure control command values to keep to predetermined levels the hydraulic pressures supplied to the frictional engaging devices at the beginning of the inertia phase thus recognized; and pressure control command value output apparatus for outputting to the pressure control command generation apparatus the pressure control command values calculated by the torque fluctuation suppression apparatus.
Other objects and further features of the invention will be apparent from the following detailed description when read in conjunction with the accompanying drawings.